Transient Hygrothermal-Response of Power Modules in Inverters—The Basis for Mission Profiling Under Climate and Power Loading

Abstract

The number of outdoor applications of power electronics is growing. Therefore, mission profiling with respect to climate conditions has become a new field of interest. The response of moisture inside power electronics can be simulated by the use of an equivalent circuit. It consists of variable and controlled resistors and capacitors to describe diffusivity, permeability, and storage in polymers. Here, voltages represent the concentration of moisture in air or polymers. Such R-C networks allows us to describe 2-D- and 3-D-effects. The coupling to the thermal equivalent networks can be done by voltage outputs, e.g., temperatures. The coupled thermal- and hygro-sub-circuit lead to the overall hygrothermal equivalent circuit. This circuit allows simulating moisture levels based on climate conditions and heating due to the operation of power electronics. Examples demonstrate the possibility that humidity inside cabinets exceeds the ambient conditions due to the desorption of moisture from the heated polymers. It is also demonstrated that condensation of moisture can occur during day and night cycles. Failure models need to be established to conclude with lifetime calculations based on this method.